Effect of conventional finishing on cloth surface color

Finishing is the last process of dyeing and finishing process, which is mainly responsible for processing grey cloth into finished cloth to meet the needs of various customers, and provide qualified clothing fabrics for garment factories. For yarn-dyed fabric, its production processes include: singeing, desizing, mercerizing, washing, styling, adding color, raising, grinding, calendering, resin, coating, pre-shrinking.

1, singeing: mainly to burn the surface of the cloth fluff, so that the cloth surface clean. It has little effect on the color of cloth.

2, desizing: through the action of enzymes and high temperature washing to remove the stock on the grey cloth. It has little effect on the color of the cloth, but it is necessary to pay attention to the influence of the whitening agent on the color of some white cloth when the high temperature desizing.

3, mercerization: Mercerization is the use of concentrated alkali on cotton fibers to increase the luster of cotton, strength and so on. Usually makes the cloth color darker, and with the increase of mercerine concentration, the degree of cloth color darker also increases.

4. Washing: For BLUE R dye fabric, the washing fastness of the dye is decreased due to the action of alkali after mercerization. In order to ensure the washing fastness of the finished product, the finishing should be washed after mercerization. It can be seen that the fabric containing BLUE R dye will be lighter and less blue after washing.

5, soft shaping: some softeners because of their self-crosslinking properties, when shaping the fabric surface film, so it has a certain deepening effect, but the difference is not obvious. In addition, if the sublimation fastness of disperse dyes is not good at high temperature, it may affect the color light and fastness due to the migration of dyes to the surface.

6, adding color: the color of the cloth and the standard difference between the net color or approximately net color cloth, can be adjusted by dyeing.

7, pre-shrinking: Pre-shrinking is the method of shrinking the fabric through mechanical action to meet customer requirements, and has little impact on color

Effect of alkali strip on finishing

Due to the gradual rise in water cost, cotton and other cellulose fiber fabrics are more likely to have alkali on semi-finished fabrics before dyeing and finishing, and even the PH value of the dyed fabric is above 8, and some even exceed 9. Among them, the continuous long car pad dyeing production line is more frequent than the intermittent immersion dyeing method.

After dyeing and before post-treatment, the semi-product grey cloth with alkali phenomenon will have a greater adverse effect on the more auxiliary varieties in the post-treatment and post-finishing, and sometimes it is very far-reaching (such as the textile finished products dyed with some reactive dyes that are not alkali hydrolytic, a few months later, the wind printing and other discoloration problems will still occur due to the alkali on the cloth surface).

Because of the defects revealed in the post-processing and post-finishing, it is difficult to find the cause of the problem, which is easy to mislead and misjudge, and the attention is blindly focused on the post-processing and post-finishing additives.

1, the impact on some post-processing additives

Post-treatment generally refers to the process content of washing, soaping, color fixing (or cross-chain agent treatment) after the completion of the dyeing process. For the dyeing of reactive dyes, it is necessary to remove the floating color fully after soap washing, in order to reveal a stable real dyeing color. Fixing color is to improve the color fastness and other internal quality indicators taken, although some fixing agents will produce a certain shift in the color of the color light, but this should be controlled in advance when the lofting work, and increase the color fastness is the first purpose of fixing color.

However, some commonly used important color fixing agents, cross-chain agent varieties, most of the most suitable working bath pH value in 5 ~ 6.5 weak acidity, in the alkaline medium, the higher the PH value, the worse the effect, to a certain alkalinity and even precipitate precipitation.

Poor working conditions will not get the due effect, so that the color fastness and other indicators can not be satisfactorily improved. At this time, even if the amount of fixing agent or cross-chain agent is increased, the improvement of fastness does not show synchronization, so it loses the significance of increasing the amount of additives.

2, the impact on the after-finishing additives

Finishing is the last link in the three major links of dyeing and finishing engineering, which is of great significance to the function expansion, function extension and grade improvement of textiles.

Some important auxiliaries on the finishing, such as silicone softener, non-ironing resin finishing agent, etc., are also similar to color fixing agent and crosslinking agent auxiliaries, and need to be treated in a weakly acidic working bath to be more suitable. The difference is that the taboo of silicone softeners is not that the alkali agent can directly destroy the silicone oil that makes the fiber soft, but that the emulsified softener can have a demulsification effect. Pure organic silicone oil can not be used directly on textiles, so it is necessary to use the emulsification method to make the emulsion (or microemulsion) of silicone oil content is generally 10 to 15%, in order to become a truly usable commodity softener.

Alkali agent to emulsified softener can produce demulsification, so that emulsifier failure and precipitated silicone oil, with the advance of time, separated and precipitated silicone oil points, after repeated aggregation, and the formation of large diameter, visible to the naked eye oil droplets, even in serious cases, there will be oil bleaching phenomenon. After the separated silicone oil stains the fabric, it will form oil spots of different sizes. What is more serious is that the combination of organic silicone oil and fiber makes the stripping and repair of such defects quite difficult, so only prevention is more important than treatment, it has positive practical significance.

In addition, in the ironing finishing resin, which occupies an important position in the post-finishing, acidic catalytic conditions are required when used, so it is quite critical to ensure that the PH value of the working bath of the rolling groove is in the specified range.

The various items of post-finishing are basically the continuous way of rolling and dipping, which has the advantages of high efficiency, fast speed, and almost 100% utilization of raw materials. If the semi-product is coated with alkali, it will have a cumulative effect on the working bath in the rolling tank, so that the pH value of the working liquid will gradually rise. Therefore, there is often no problem at the beginning of the car, after 2000 ~ 3000m, Zhezhe problems, and more and more serious, which for the lack of field experience, easy to produce illusion and misjudgment. Starting only from the surface phenomenon, only from the additives to find the cause, not only can not solve the problem, but also will eventually be confused.

After finishing the various finishing items, most of the fastness and durability are very good, few can be effectively used for stripping supporting chemical agents, which makes the defects once they occur, it is difficult to effectively repair, so compared with the problem of post-processing, the consequences are more serious.

3, cause the cloth with alkali prone factors

In the pre-treatment and dyeing of cellulose fibers, they are basically carried out in a working bath with a higher pH value. Due to the effect of caustic soda, soda ash and other alkali agents, the cellulose fiber has a great directness (affinity), coupled with the excellent water absorption of cellulose fiber, so to the fiber has been fully permeated and adsorbed alkali agent for cleaning, need a lot of water to wash, which in addition to a lot of cold water, but also need to use hot water, sometimes also acid and alkali neutralization to give cooperation. Since the water consumption, energy consumption and removal efficiency of the alkali-removing process are basically a proportional relationship, pre-treatment and dyeing are also the main links of water and energy consumption. This is the performance characteristics of natural cellulose fibers such as cotton and alkali agents, and the relationship between them, so far, fabric dyeing and finishing processing is also inseparable from alkali agents.

(2) The working mode of mechanical equipment also directly determines the washing efficiency, different washing methods, such as immersion type, spray type, recoil-overflow, shock type (ultrasonic), etc., have their different varieties of adaptability, different equipment types of washing efficiency effect is different. In the production of washing equipment, it is required to save water, use steam, and have a good cleaning effect, but there is a certain contradiction between the two. For the fiber cleaning alkali, to ensure the quality of the product is its basic principle. Otherwise, repair after the occurrence of defects will not be worth the loss but lead to greater consumption and waste of water, energy, and other raw materials. To ensure a success is one of the most fundamental measures to save water and energy.

Water saving and energy saving in dyeing and finishing is a goal that has almost no end. First of all, the design of mechanical equipment must be considered, the starting point, purpose and goal of its design, the working principle of equipment operation, should meet the requirements of the dyeing and finishing process as far as possible. For the cleaning efficiency, water saving and energy saving effect, only after large-scale production and use, the conclusion is reliable. The process plan of dyeing and finishing application must also be based on the performance characteristics of the equipment, and a suitable targeted process must be developed. Therefore, in addition to the understanding of the properties and properties of relevant chemical raw materials, dyeing and finishing personnel also need to understand the equipment. Reasonable process plan and flow can not only ensure the washing efficiency, but also make it possible to reduce the number of washing times and process time.

④ After detection, it can be found that the pH value of the cloth surface of the dyed semi-products (including the final dyed products) after dyeing and post-processing, even in the same production line, is also fluctuating. In general, defects in mechanical equipment and process design, once problems occur, will be batch, and problems in operation and site management are dynamic changes. Therefore, this is also a management can not miss the focus. After long-term observation, it can also be found that the problem on the washing is similar to the problem in the pre-treatment process, and has a certain seasonal periodicity, and the fluctuation is especially frequent in the winter when the weather temperature is low.

The water temperature of washing has a significant impact on the dissolution of chemical raw materials such as alkali agents (including auxiliaries), so there is no lack of hot water washing in the cleaning work. You can see some liquid additives, there are many varieties in the summer is very easy to flow thin solution, it is easy to form a uniform working liquid, but the same additives in the winter, it will become a high viscosity thick, chemical material becomes more difficult. Correspondingly, when it comes to the cleaning process, the cleaning water of different water temperatures will not have the same cleaning efficiency.

Soda ash even in the summer, with room temperature cold water is easy to absorb into the crystal water molecules, and the formation of low temperature water is difficult to dissolve solid alkali precipitation, when the hot water 50 ~ 60℃ or above, it will dissolve fully and there will be no old alkali generation. In the winter, the water temperature of the cold water is very low, if the water temperature and the number of times of washing can not be distinguished, the cleaning efficiency will naturally decline accordingly. Hot water penetrates cellulose fibers much better than cold water, so there is a saying that "the cheapest penetrant is hot water." Since hot water can improve solubility and promote permeability, it further enhances and strengthens the cleaning basis for alkali agents. Therefore, it can be seen that similar defects in pre-treatment are often related to poor chemical materials and poor cleaning afterwards, and are often prone to occuring in winter.

Therefore, if the front-line car operators have insufficient understanding of the problem of washing, think that washing has nothing to do with the overall situation and treat it casually, or even think that it has little impact on color and color, and can not cause enough attention in terms of process parameters such as water temperature, water quantity, washing times, washing time, etc., the adverse effects will be difficult to avoid.

5. Because the fabric is treated for a long time in the working bath of the two links of pre-treatment and dyeing, the penetration and absorption of alkali on the fiber has been extremely thorough. On the continuous pad dyeing production line where the blank cloth is subjected to great tension, there is still a problem that surface cleaning is easy to occur, especially for some high-density and heavy grey cloth. In this regard, in addition to cleaning should be strengthened, neutralization treatment should also be a useful supplement.

It should also be noted that in addition to the variability of grey cloth and fiber types, changes in water quality, and failures in equipment and supporting facilities are often possible objective phenomena, coupled with the possibility of subjective interference such as process execution, resulting in semi-finished grey cloth with alkali will also be dynamic and often irregular. Therefore, the timing detection and correction of the pH value of the working bath of the rolling groove in the field management should be set as the process specification.

Post-finishing is not only related to the change of color before and after dyeing, but also if the corresponding measures are not done after dyeing, resulting in an abnormal pH range, resulting in quality problems, PH value is one of the key conditions of chemical reaction, so it is also listed as one of the four process conditions on dyeing and finishing production. The alkali-carrying of dyed semi-products has a negative effect on many auxiliaries in post-treatment and post-finishing, although the mechanism of its influence is different, it is common that it will produce sequelae. The cause of alkali on semi-finished grey cloth, from the surface, of course, is related to washing, but different washing machinery, process measures and washing efficiency are inextricably related to it. This problem seems to be a small matter, but the negative impact of the legacy is very wide, and many quality problems of dyeing products are related to this, so it must be paid full attention to.